1. Field of the Invention
The present invention relates to downhole technology for the oil and gas industry, and in particular to an improved apparatus for running on a workstring and method of actuation. In various aspects, the apparatus relates to a wellbore plug, an auto-fill device, and a method of running a tubing string.
2. Description of Related Art
During the lifetime of an oil/gas production well, various servicing operations will be carried out to the well to ensure that the efficiency and integrity of the well is maximised. These include a full work over, surface well-head tree change, side tracking or close proximity drilling operations. To allow these operations to be done safely and to accommodate verification pressure tests from surface, it is necessary to install a plug (or plugs) into the production tubing to create a barrier to both test against and provide isolation from the production zones.
These plugs are typically run into or retrieved from the wellbore on wireline or tubing strings. When running the plug in the wellbore, it may be difficult to locate the plug and/or its associated packer effectively in the correct location where there is fluid pressure beneath the plug.
Similar difficulties may arise when tubing strings, such as completion strings, are run against fluid pressure in the well. Open-ended strings will simply fill with wellbore fluid as they are run, but in many applications the tubing string will not be open, and will be positively buoyant. Auto-fill devices, which may take the form of plugs, are used to allow controlled fluid flow into a tubing string during run in.
When retrieving plugs it is necessary to equalize pressure above and below prior to unlocking and removal. Various types of pressure equalising devices have been developed, including those known as “pump open plugs” and “pressure cycle plugs”. These plugs are run in with sealed ports in a closed position, and after they have served their purpose in the intervention, are opened to allow fluid flow and pressure equalisation between regions above and below the plug.
The sealed ports must resist large pressure gradients, and therefore must have high integrity. Exposure of conventional seals to wellbore fluids risks compromise to their integrity, and will not generally be acceptable. This precludes running of conventional plugs in an open configuration in which the seals would be exposed.